The broad objective of this project is to elucidate the molecular mechanisms which regulate protein synthesis during early development in the sea urchin. Fertilization results in a 20-40 fold increase in the rate of protein synthesis. This increase is mediated by the mobilization of stored maternal mRNA into polysomes. It is now clear that the mechanism which regulates this process operates at two discrete levels. The first is at the level of activity of the mRNA itself. Inactive mRNAs in the unfertilized egg appear to be in a repressed form, presumably due to the action of a protein repressor bound to the mRNA. This is popularly known as the "masked message hypothesis". One of the major goals of this proposal is to isolate and characterize the mRNA repressor. In addition we will identify and attempt to ascribe functional roles to the other protein constituents of the mRNPs (messenger ribonucleoprotein particles). The second level of regulation is at the level of changes in the activity of components of the translational machinery such as initiation factors or ribosomes. The activity of at least one and probably more components of the translational machinery increase after fertilization. This results in an increase in the capacity to translate mRNA. We will attempt to identify components whose activity regulates translational capacity. It appears that the interaction of these two levels of regulation account for much of the complex translational regulation seen during early development.